The present invention relates to a circuit for detecting an NTSC (National Television System Committee) signal or a PAL (Phase Alternation by Line) signal in a laser disk player system, and more particularly to a circuit for detecting the presence of an NTSC or PAL signal by using a waveform shaped FM (Frequency Modulation) video signal shaped.
Generally, in a laser disk player system, a video signal recorded on a disk is picked up, and an NTSC or PAL signal is detected from an FM-demodulated signal. NTSC and PAL signals have different frequency bands. An example of such a disk player system is shown in U.S. Pat. No. 4,914,523 issued Apr. 3, 1990 to Maruta and entitled OPTICAL DISK APPARATUS COMPATIBLE WITH DIFFERENT TELEVISION SYSTEM STANDARDS. U.S. Pat. No. 4,914,523 discloses an optical disk player for use with optical disks having color video information recorded thereon, which avoids playing back an optical disk on which is recorded color video information according to a TV system other than that for which the player is intended.
The NTSC video signal has a frequency spectrum such as shown in FIG. 1. There are 525 horizontal synchronizing signals per second, and 60 vertical synchronizing signals per second. The PAL video signal has a frequency spectrum such as shown in FIG. 2. Here, there are 625 horizontal synchronizing signals per second and 50 vertical synchronizing signals per second.
FIG. 3 is a circuit diagram for detecting the NTSC or PAL signal in a conventional laser disk player system. Referring to FIG. 3, an optical pick-up part 1 picks up a video signal from the disk and outputs a signal to an FM video signal processing part 2. The waveform of the video signal outputted from the optical pick-up part 1 is shaped by the FM video signal processing part 2. The FM video signal is demodulated by an FM video signal demodulator 3, and then is outputted as a composite video signal. A synchronization separator 4 receives the composite video signal and separates a synchronizing signal from the composite video signal. A synchronization detector 5 receives the synchronizing signal and detects the horizontal synchronizing signal or the vertical synchronizing signal. A MICOM (micro-computer) 6 receives the horizontal synchronizing signal or the vertical synchronizing signal outputted from the synchronization detector 5, and detects the presence of an NTSC or a PAL signal by counting the synchronizing signal. For example, the MICOM 6 inputs the horizontal synchronizing signal separated from the synchronization separator 4, counts the horizontal synchronizing signal, and if the horizontal synchronizing signal is 525 per second, the MICOM 6 detects the presence of an NTSC signal. If the horizontal synchronizing signal is 625 per second, the MICOM 6 detects the presence of a PAL signal. However, if the MICOM 6 inputs the vertical synchronizing signal separated from the synchronization separator 4 and counts the vertical synchronizing signal, and if the vertical synchronizing signal is 60 per second, the MICOM 6 detects the presence of an NTSC signal. If the vertical synchronizing signal is 50 per second, the MICOM 6 detects the presence of a PAL signal.
Meanwhile, in FIG. 3, which shows the conventional circuit for detecting the presence of an NTSC or a PAL signal, the synchronizing signal is obtained after the FM video signal demodulator outputs the composite video signal, after which the synchronizing signal is counted and detected. Therefore, since there is necessarily a waiting time during the counting of the synchronizing signal, not only is the speed for detecting the NTSC or PAL signal diminished, but also transient phenomena are experienced by a servo part of the disk during the waiting period. Therefore, there are problems in the conventional NTSC or PAL signal detecting circuit.